Nitric oxide (NO) has recently been implicated in a variety of bioregulatory processes, including normal physiological control of blood pressure, macrophage-induced cytostasis and cytotoxicity, and neurotransmission (Moncada et al., "Nitric Oxide from L-Arginine: A Bioregulatory System," Excerpta Medica, International Congress Series 897 (Elsevier Science Publishers B.V.: Amsterdam, 1990); Marletta et al., "Unraveling the Biological Significance of Nitric Oxide," Biofactors, 2, 219-225 (1990); Ignarro, "Nitric Oxide. A Novel Signal Transduction Mechanism for Transcellular Communication," Hypertension (Dallas), 16, 477-483 (1990)). A number of compounds have been developed which are capable of delivering nitric oxide, including compounds which release nitric oxide upon being metabolized and compounds which release nitric oxide spontaneously in aqueous solution.
Those compounds which release nitric oxide upon being metabolized include the widely used nitrovasodilators glyceryl trinitrate and sodium nitroprusside (Ignarro et al., J. Pharmacol. Exp. Ther., 218, 739-749 (1981); Ignarro, Annu. Rev. Pharmacol. Toxicol., 30, 535-560 (1990); Kruszyna et al., Toxicol. Appl. Pharmacol., 91, 429-438 (1987); Wilcox et al., Chem. Res. Toxicol., 3, 71-76 (1990). Another compound, S-nitroso-N-acetylpenicillamine, has been reported to release nitric oxide in solution and to be effective at inhibiting DNA synthesis (Garg et al., Biochem. and Biophys. Res. Comm., 171, 474-479 (1990)).
Numerous nitric oxide-nucleophile complexes have been described, e.g., Drago, ACS Adv. Chem. Ser., 36, 143-149 (1962). See also Longhi and Drago, Inorg. Chem., 2, 85 (1963). Some of these complexes are known to evolve nitric oxide on heating or hydrolysis, e.g., Maragos et al., J. Med. Chem. 34, 3242-3247 (1991).
The cytostatic effect of nitric oxide solutions on tumor cells in vitro has been demonstrated. In particular, it has been shown that solutions of nitric oxide inhibit DNA synthesis and mitochondrial respiration of tumor cells in vitro (Hibbs et al., Biochem. and Biophys. Res. Comm., 157, 87-94 (1988); Stuehr et al., J. Exp. Med., 169, 1543-1555 (1989)).
Endothelium-derived relaxing factor (EDRF) is a labile humoral agent which is part of a cascade of interacting agents involved in the relaxation of vascular smooth muscle. EDRF is thus important in the control of vascular resistance to blood flow and in the control of blood pressure. Some vasodilators act by causing EDRF to be released from endothelial cells. (See Furchgott, Ann. Rev. Pharmacol. Toxicol., 24, 175-197 (1984).) In 1987, Palmer et al., presented evidence that EDRF is identical to the simple molecule, nitric oxide, NO (Nature, 317, 524-526 (1987)), though more recently, that conclusion has been challenged (Myers et al., Nature, 345, 161-163, 1990)).
Nitric oxide in its pure form, however, is a highly reactive gas having limited solubility in aqueous media (WHO Task Group on Environmental Health Criteria for Oxides of Nitrogen, Oxides of Nitrogen, Environmental Health Criteria 4 (World Health Organization: Geneva, 1977)). Nitric oxide, therefore, is difficult to introduce reliably into most biological systems without premature decomposition.
The difficulty in administering nitric oxide can be overcome in some cases by administering nitric oxide pharmacologically in prodrug form. The compounds glyceryl trinitrate and sodium nitroprusside are relatively stable and release nitric oxide only on activation (Ignarro et al., J. Pharmacol. Exp. Ther., 218, 739-749 (1981); Ignarro, Annu. Rev. Pharmacol. Toxicol., 30, 535-560 (1990); Kruszyna et al., Toxicol. Appl. Pharmacol., 91, 429-438 (1987); Wilcox et al., Chem. Res. Toxicol., 3, 71-76 (1990)). While this feature may be an advantage in some applications, it can also be a significant liability, as in the development of tolerance to glyceryl trinitrate via the exhaustion of the relevant enzyme/cofactor system (Ignarro et al., Annu. Rev. Pharmacol. Toxicol., 25, 171-191 (1985); Kuhn et al., J. Cardiovasc. Pharmacol., 14 (Suppl. 11), S47-S54 (1989)) and toxicity from metabolically produced cyanide during prolonged administration of nitroprusside (Smith et al., "A Potpourri of Biologically Reactive Intermediates" in Biological Reactive Intermediates IV. Molecular and Cellular Effects and Their Impact on Human Health (Witmer et al., eds.), Advances in Experimental Medicine and Biology Volume 283 (Plenum Press: New York, 1991), pp. 365-369).
Evidence that nitric oxide is released from the endothelial cells and is responsible for the relaxation of the vascular smooth muscle, and hence the control of blood pressure, has resulted in the development of artificial agents that can deliver nitric oxide in vivo. A very important class of such agents is the nitric oxide-nucleophile complexes. Recently, a method for treating cardiovascular disorders in a mammal with certain nitric oxide-nucleophile complexes was disclosed, e.g. in U.S. Pat. No. 4,954,526. These compounds contain the anionic N.sub.2 O.sub.2.sup.- group or derivatives thereof. See also, Maragos et al., J. Med. Chem., 34, 3242-3247 (1991). Many of these compounds have proven especially promising pharmacologically because, unlike nitrovasodilators such as nitroprusside and nitroglycerin, they release nitric oxide without first having to be activated. The only other series of drugs currently known to be capable of releasing nitric oxide purely spontaneously is the S-nitrosothiol series, compounds of structure R--S--NO (Stamler et al., Proc. Natl. Acad. Sci. U.S.A., 89, 444-448 (1992); Stamler et al., Proc. Natl. Acad. Sci. U.S.A., 89, 8087-8091 (1992)); however, the R--S.fwdarw.NO--NO reaction is kinetically complicated and difficult to control (Morley et al., J. Cardiovasc. Pharmacol., 21, 670-676 (1993)). The N.sub.2 O.sub.2.sup.- containing compounds are thus advantageous among drugs currently known in that they decompose at any given pH via a cleanly first order reaction to provide doses of nitric oxide that can be predicted, quantified, and controlled. See, e.g., Maragos et al., J. Med. Chem., 34, 3242-3247 (1991).
Nitric oxide/nucleophile complexes which release nitric oxide in aqueous solution are also disclosed in U.S. Pat. Nos. 5,039,705, 5,185,376, 5,155,137, 5,208,233, 5,212,204, 5,250,550 and 5,366,997 (issue date Nov. 22, 1994) as well as in pending U.S. patent applications Ser. Nos. 07/764,908 (filed Sep. 24, 1991), (now abandoned) 07/858,885 (filed Mar. 27, 1992) (now U.S. Pat. No.5,389,675, issued Feb. 14, 1995), 07/867,759 (filed Apr. 13, 1992) (now abandoned), 07/935,565 (filed Aug. 24, 1992) (now U.S. Pat. No.5,405,919, issued Apr. 11, 1995), 08/017,270 (filed Feb. 12, 1993) (now abandoned), and 08/121,169 (filed Sep. 14, 1993) (now U.S. Pat. No. 5,525,357, issued Jun. 11, 1996) as useful therapeutic agents (see also Maragos et al., J. Med. Chem., 34, 3242-3247 (1991)).
Despite the promise of the nitric oxide/nucleophile adducts that have been investigated, their pharmacological application has been limited by their tendency to distribute evenly throughout the medium. Such even distribution is a great advantage in many research applications, but tends to compromise their selectivity of action. Another limitation to the application of these nitric oxide/nucleophile adducts is their propensity for relatively rapid release of nitric oxide which may necessitate frequent dosing to achieve a prolonged biological effect. Thus there remains a need for nitric oxide-releasing compositions which are capable of concentrating the effect of the nitric oxide release to a situs of application and for which nitric oxide release may be controlled for effective dosing.
It is, therefore, a principal object of the present invention to provide a polymeric composition comprising a biopolymer to which is bound a N.sub.2 O.sub.2.sup.- functional group and which is capable of releasing NO under physiological conditions. Another object of the invention is to provide a polymeric composition comprising a biopolymer to which is bound a N.sub.2 O.sub.2.sup.- functional group whose release of NO can be controlled such that local or cell/tissue specific release can be effected. It is another object of the present invention to provide a polymeric composition comprising a biopolymer to which is bound a N.sub.2 O.sub.2.sup.- functional group whose release of NO is such that a prolonged biological effect can be attained. Yet another object of the present invention is to provide pharmaceutical compositions comprising such biopolymeric compositions. It is also an object of the present invention to provide a method of treating a biological disorder involving the administration of such biopolymeric compositions. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.